1. Field of the Invention
This invention relates to electrophotography, and more particularly to an electrophotographic process for forming a latent charge image on one surface of a recording medium.
2. Description of the Prior Art
Electrophotography used for forming a latent charge image on a recording medium is generally classified into two types. In one type of electrophotography, such a latent charge image is formed directly on one surface of a photoconductor layer, while in the other type of electrophotography, such a latent charge image is formed on the surface of an electrical insulator layer provided on one surface of a photoconductor layer.
A plurality of latent image forming processes have been proposed for the latter type of electrophotography. One of the proposed processes employes a recording medium which is prepared by disposing a photoconductor layer on a conductive support and covering the photoconductor layer with a transparent electrical insulator layer. In the first step of this process, the surface of the transparent insulator layer is uniformly charged with charges of one polarity in a dark place. Generally, negative and positive charges are applied respectively when the photoconductor is of n-type and p-type. Then, an optical image is projected on the recording medium by exposing the recording medium to light reflected from the original image. As a result, the photoconductor layer is rendered conductive in the areas exposed to light, and the charges migrate to the boundary between the insulator layer and the photoconductor layer in these areas. Charges of opposite polarity are then applied in the dark places so as to substantially eliminate the surface charges in the areas exposed to light. As a result, the charge density on the surface of the insulator layer portions not exposed to light becomes higher than that on the surface of the insulator layer portions exposed to light. When, finally, the entire surface of the insulator layer is uniformly exposed to light, a charge distribution corresponding to the amount of surface charges is produced at the boundary between the insulator layer and the photoconductor layer. Thus, a potential distribution corresponding to the surface charges can be obtained. However, this latent image forming process has been defective in that the density of the developed image is not satisfactory and fogging tends to occur in the developed image since the contrast of the latent image potentials is not so marked and application of the charges of opposite polarity is difficult to control resulting in unstable charging.